def complete_bracket_sequence(input_string):
    # Step 1: Parse the input string to separate the individual brackets. Output the parsed brackets.
    brackets = input_string.split()
    print("Parsed brackets:", brackets)

    # Step 2: Initialize a stack to keep track of the opening brackets.
    stack = []

    # Step 3: Process each bracket in the input string. If the bracket is an opening bracket, push it onto the stack. If it is a closing bracket, pop the stack and check that the popped bracket matches the closing bracket. If the stack is empty or the brackets do not match, there is an error in the input string. Output the current bracket, the action taken (push or pop), and the current state of the stack after each action.
    for bracket in brackets:
        if is_opening_bracket(bracket):
            stack.append(bracket)
            print(f"Push {bracket} onto stack. Stack: {stack}")
        else:
            if not stack or not brackets_match(stack[-1], bracket):
                print("Error: mismatched or missing bracket.")
                return None
            stack.pop()
            print(f"Pop {bracket} from stack. Stack: {stack}")

    # Step 4: After processing all brackets in the input string, check if the stack is empty. If it is not, pop each remaining opening bracket from the stack and append the corresponding closing bracket to the output string. Output the current state of the stack and the output string after each action.
    output_string = ""
    while stack:
        opening_bracket = stack.pop()
        closing_bracket = get_matching_closing_bracket(opening_bracket)
        output_string += closing_bracket + " "
        print(f"Pop {opening_bracket} from stack and append {closing_bracket} to output. Stack: {stack}, Output: {output_string}")

    # Step 5: Return the output string, which contains the completed sequence of brackets.
    return output_string.strip()